Nonaqueous electrolyte solution, and lithium ion secondary battery having the same

ABSTRACT

The exemplary embodiment has an object to provide a nonaqueous electrolyte solution having a flame retardancy over a long period and having a good capacity maintenance rate. The exemplary embodiment is a nonaqueous electrolyte solution containing a lithium salt, at least one oxo-acid ester derivative of phosphorus selected from compounds represented by a predetermined formula, and at least one disulfonate ester selected from a cyclic disulfonate ester and a linear disulfonate ester represented by the predetermined formulae.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. application Ser. No. 13/578,209, filedAug. 9, 2012, which is the National Stage Entry of InternationalApplication No. PCT/JP2011/052934, filed Feb. 10, 2011, which claimsbenefit of Japanese Patent Application No. 2010-027056, filed Feb. 10,2010, the contents of all of which are incorporated herein by referencein their entirety.

TECHNICAL FIELD

The present invention relates to a nonaqueous electrolyte solution, anda lithium ion secondary battery having the same.

BACKGROUND ART

Since lithium ion secondary batteries, which are devices having anonaqueous electrolyte solution, can achieve high energy densities, theyattract attention as batteries for cell phones, batteries for notebookcomputers, batteries for large power storage, and batteries forautomobiles.

Although lithium ion secondary batteries can achieve high energydensities, up-sizing makes the energy gigantic, and higher safety isdemanded. For example, in large power sources for power storage andpower sources for automobiles, especially high safety is demanded.Therefore, safety measures are applied such as the structural design ofcells, packages and the like, protection circuits, electrode materials,additives having an overcharge protection function, the reinforcement ofshutdown function of separators, and the like.

Lithium ion secondary batteries use aprotic solvents such as cycliccarbonates and linear carbonates as an electrolyte solvent; and thesecarbonates are likely to have a low flash point and be combustiblethough having a high dielectric constant and a high ionic conductivityof lithium ions.

A technology is known which uses as an additive a substance reductivelydecomposed at a higher potential than carbonates used as electrolytesolvents and forming an SEI (Solid Electrolyte Interface) being aprotection membrane having a high lithium ion permeability. The SEI haslarge effects on the charge/discharge efficiency, the cyclecharacteristics and the safety. The SEI can further reduce theirreversible capacity of carbon materials and oxide materials.

One of means to further enhance the safety of lithium ion secondarybatteries includes making electrolyte solutions flame retardancy. PatentLiterature 1 discloses an organic electrolyte solution secondary batteryusing a phosphate triester as a main solvent of an organic electrolytesolution and having a negative electrode of a carbon material as aconstituting element.

Patent Literature 2 discloses that the use of a mixed solvent of aspecific halogen-substituted phosphate ester compound and a specificester compound as an electrolyte solvent can provide an electrolytesolution having a low viscosity and excellent low-temperaturecharacteristics. Patent Literature 3 discloses a method formanufacturing a nonaqueous electrolyte battery by using a nonaqueouselectrolyte solution containing vinylene carbonate and 1,3-propanesultone added therein. Patent Literature 4 discloses a battery having anonaqueous electrolyte solution which contains a predetermined amount ofphosphate esters having fluorine atoms in molecular chains thereof, andsalts in a concentration of 1 mol/L or higher, has a viscosity of lowerthan 6.4 mPa·s. The disclosure contends that making such a constitutioncan provide a battery having an excellent flame retardancy, aself-extinguishing property and high-rate charge/dischargecharacteristics.

Patent Literature 5 discloses a nonaqueous electrolyte solutioncontaining at least one phosphate ester derivative represented by apredetermined formula, a nonaqueous solvent and a solute. PatentLiterature 6 discloses that the use of a fluorophosphate ester compoundas a nonaqueous electrolyte solution can provide an electrolyte solutionbeing excellent in the conductivity and the reduction resistance, anddeveloping a high flame retardancy even in a low blend amount.

Patent Literature 7 discloses a nonaqueous electrolyte solution obtainedby dissolving a lithium salt in a nonaqueous solvent containing aphosphate ester compound, a cyclic carbonate ester containing a halogen,and a linear carbonate ester.

CITATION LIST Patent Literature

Patent Literature 1: JP2908719B

Patent Literature 2: JP3821495B

Patent Literature 3: JP2007-059192A

Patent Literature 4: JP2007-258067A

Patent Literature 5: JP3422769B

Patent Literature 6: JP2006-286277A

Patent Literature 7: JP3961597B

SUMMARY OF INVENTION Technical Problem

However, in Patent Literature 1, a phosphate ester is reductivelydecomposed on a carbon negative electrode during long-term usage, and aresistance rise due to the deposition of the reductant on the electrode,a resistance rise due to the generation of gases, and the like arecaused, largely decreasing battery characteristics in some cases.Further a problem is posed in which the phosphate ester is reductivelydecomposed during usage, and the flame retardancy of the electrolytesolution decreases in some cases.

In Patent Literatures 2 to 6, although there are descriptions about theflame retardancy of electrolyte solutions and the initialcharacteristics of batteries, there is no reference to the long-termreliability of the batteries. There is further a problem in which ahalogen-substituted phosphate ester and a derivative thereof as well arereductively decomposed gradually on a negative electrode duringlong-term usage, causing a decrease in battery characteristics due to aresistance rise in some cases, and as a result of the reductivedecomposition, the flame retardancy of the electrolyte solutionsdecreases in some cases. Particularly, even in the case where vinylenecarbonate or 1,3-propane sultone is added as an additive to form an SEIas shown in Patent Literature 3, a sufficient life cannot be obtained insome cases. There is no reference to the flame retardancy over a longperiod.

Patent Literature 7 describes that a halogen-substituted cycliccarbonate ester can form a film containing the halogen on a negativeelectrode, and the reductive decomposition of a phosphate ester or ahalogen-substituted phosphate ester can be suppressed. However, in thecase where the reductive decomposition of a phosphate ester or ahalogen-substituted phosphate ester is intended to be suppressed over along period only by a halogen-substituted cyclic carbonate ester, alarge amount of the halogen-substituted cyclic carbonate ester becomesnecessitated, and a decrease in the ionic conductivity of an electrolytesolution is caused in some cases. There are further cases where a largeresistance rise and a decrease in the capacity maintenance rate ofbatteries in a long period are caused.

Thus, the exemplary embodiment has an object to provide a nonaqueouselectrolyte solution having a flame retardancy over a long period andhaving a good capacity maintenance rate.

Solution to Problem

One exemplary embodiment is a nonaqueous electrolyte solution,comprising:

a lithium salt;

at least one oxo-acid ester derivative of phosphorus selected fromcompounds represented by the formulae (1) to (3); and

at least one disulfonate ester selected from a cyclic disulfonate esterrepresented by the formula (4) and a linear disulfonate esterrepresented by the formula (5).

In the formula (1), R₁₁, R₁₂ and R₁₃ each independently represent anygroup selected from an alkyl group, an aryl group, an alkenyl group, acyano group, a phenyl group, an amino group, a nitro group, an alkoxygroup and a cycloalkyl group, and a halogen-substituted group thereof;and any two or all of R₁₁, R₁₂ and R₁₃ may be bonded to form a cyclicstructure.

In the formula (2), R₂₁ and R₂₂ each independently represent any groupselected from an alkyl group, an aryl group, an alkenyl group, a cyanogroup, a phenyl group, an amino group, a nitro group, an alkoxy groupand a cycloalkyl group, and a halogen-substituted group thereof; and R₂₁and R₂₂ may be bonded to form a cyclic structure; and X₂₁ represents ahalogen atom.

In the formula (3), R₃₁ represents any group selected from an alkylgroup, an aryl group, an alkenyl group, a cyano group, a phenyl group,an amino group, a nitro group, an alkoxy group and a cycloalkyl group,and a halogen-substituted group thereof; and X₃₁ and X₃₂ eachindependently represent a halogen atom.

In the formula (4), Q represents an oxygen atom, a methylene group or asingle bond; A₁ represents a substituted or unsubstituted alkylene grouphaving 1 to 5 carbon atoms which may be branched, a carbonyl group, asulfinyl group, a substituted or unsubstituted perfluoroalkylene grouphaving 1 to 5 carbon atoms which may be branched, a substituted orunsubstituted fluoroalkylene group having 2 to 6 carbon atoms which maybe branched, a substituted or unsubstituted alkylene group having 1 to 6carbon atoms which contains an ether bond and may be branched, asubstituted or unsubstituted perfluoroalkylene group having 1 to 6carbon atoms which contains an ether bond and may be branched, or asubstituted or unsubstituted fluoroalkylene group having 2 to 6 carbonatoms which contains an ether bond and may be branched; and A₂represents a substituted or unsubstituted alkylene group, a substitutedor unsubstituted fluoroalkylene group, or an oxygen atom.

In the formula (5), R₁ and R₄ each independently represent an atom or agroup selected from a hydrogen atom, a substituted or unsubstitutedalkyl group having 1 to 5 carbon atoms, a substituted or unsubstitutedalkoxy group having 1 to 5 carbon atoms, a substituted or unsubstitutedfluoroalkyl group having 1 to 5 carbon atoms, a polyfluoroalkyl grouphaving 1 to carbon atoms, —SO₂X₁₁ (X₁₁ is a substituted or unsubstitutedalkyl group having 1 to 5 carbon atoms), —SY₁₁ (Y₁₁ is a substituted orunsubstituted alkyl group having 1 to 5 carbon atoms), —COZ (Z is ahydrogen atom or a substituted or unsubstituted alkyl group having 1 to5 carbon atoms), and a halogen atom; and R₂ and R₃ each independentlyrepresent an atom or a group selected from a substituted orunsubstituted alkyl group having 1 to 5 carbon atoms, a substituted orunsubstituted alkoxy group having 1 to 5 carbon atoms, a substituted orunsubstituted phenoxy group, a substituted or unsubstituted fluoroalkylgroup having 1 to 5 carbon atoms, a polyfluoroalkyl group having 1 to 5carbon atoms, a substituted or unsubstituted fluoroalkoxy group having 1to 5 carbon atoms, a polyfluoroalkoxy group having 1 to 5 carbon atoms,a hydroxyl group, a halogen atom, —NX₁₂X₁₃ (X₁₂ and X₁₃ are eachindependently a hydrogen atom or a substituted or unsubstituted alkylgroup having 1 to 5 carbon atoms), and —NY₁₂CONY₁₃Y₁₄ (Y₁₂ to Y₁₄ areeach independently a hydrogen atom or a substituted or unsubstitutedalkyl group having 1 to 5 carbon atoms).

One exemplary embodiment is the nonaqueous electrolyte solutioncontaining 5% by mass or more and 60% by mass or less of the oxo-acidester derivative of phosphorus.

One exemplary embodiment is the nonaqueous electrolyte solutioncontaining 0.05% by mass or more and 10% by mass or less of thedisulfonate ester.

One exemplary embodiment is further the nonaqueous electrolyte solutioncontaining 0.5% by mass or more and 20% by mass or less of a cycliccarbonate ester containing a halogen.

One exemplary embodiment is the nonaqueous electrolyte solution gelatedwith a polymer component or a polymer.

One exemplary embodiment is a lithium ion secondary battery having thenonaqueous electrolyte solution.

One exemplary embodiment is a capacitor having the nonaqueouselectrolyte solution.

Advantageous Effects of Invention

The exemplary embodiment can provide a nonaqueous electrolyte solutionhaving a flame retardancy over a long period and having a good capacitymaintenance rate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating a constitution of a positiveelectrode of a lithium ion secondary battery. FIG. 1(a) is a plandiagram of the positive electrode, and FIG. 1(b) is a side diagram ofthe positive electrode.

FIG. 2 is a schematic diagram illustrating a constitution of a negativeelectrode of a lithium ion secondary battery. FIG. 2(a) is a plandiagram of the negative electrode, and FIG. 1(b) is a side diagram ofthe negative electrode.

FIG. 3 is a diagram illustrating a constitution of a battery elementafter being wound of a lithium ion secondary battery.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the exemplary embodiment will be described in detail.

The nonaqueous electrolyte solution according to the exemplaryembodiment comprises an aprotic solvent, a lithium salt, an oxo-acidester derivative of phosphorus, and a disulfonate ester. The exemplaryembodiment can provide a nonaqueous electrolyte solution concurrentlyhaving a high flame retardancy and a good capacity maintenance rate.

The oxo-acid ester derivative of phosphorus comprises at least oneselected from compounds represented by the following formulae (1) to(3). The oxo-acid ester derivative of phosphorus contributes to theflame retardancy of an electrolyte solution.

In the formula (1), R₁₁, R₁₂ and R₁₃ each independently represent anygroup selected from an alkyl group, an aryl group, an alkenyl group, acyano group, a phenyl group, an amino group, a nitro group, an alkoxygroup and a cycloalkyl group, and a halogen-substituted group thereof;and any two or all of R₁₁, R₁₂ and R₁₃ may be bonded to form a cyclicstructure.

In the formula (2), R₂₁ and R₂₂ each independently represent any groupselected from an alkyl group, an aryl group, an alkenyl group, a cyanogroup, a phenyl group, an amino group, a nitro group, an alkoxy groupand a cycloalkyl group, and a halogen-substituted group thereof; R₂₁ andR₂₂ may be bonded to form a cyclic structure; and X₂₁ represents ahalogen atom.

In the formula (3), R₃₁ represents any group selected from an alkylgroup, an aryl group, an alkenyl group, a cyano group, a phenyl group,an amino group, a nitro group, an alkoxy group and a cycloalkyl group,and a halogen-substituted group thereof; and X₃₁ and X₃₂ eachindependently represent a halogen atom.

A nonaqueous electrolyte solution may contain one or more oxo-acid esterderivatives of phosphorus represented by the above formulae (1) to (3).

Specific examples of compounds represented by the formula (1) include,but are not especially limited to, phosphate esters such as trimethylphosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate,dimethyl ethyl phosphate, dimethyl propyl phosphate, dimethyl butylphosphate, diethyl methyl phosphate, dipropyl methyl phosphate, dibutylmethyl phosphate, methyl ethyl propyl phosphate, methyl ethyl butylphosphate and methyl propyl butyl phosphate. The halogen-substitutedphosphate ester includes tri(trifluoroethyl) phosphate, methyl(ditrifluoroethyl) phosphate, dimethyl (trifluoroethyl) phosphate, ethyl(ditrifluoroethyl) phosphate, diethyl (trifluoroethyl) phosphate, propyl(ditrifluoroethyl) phosphate, dipropyl (trifluoroethyl) phosphate,tri(pentafluoropropyl) phosphate, methyl (dipentafluoropropyl)phosphate, dimethyl (pentafluoropropyl) phosphate, ethyl(dipentafluoropropyl) phosphate, diethyl (pentafluoropropyl) phosphate,butyl (dipentafluoropropyl) phosphate and dibutyl (pentafluoropropyl)phosphate.

Specific examples of compounds represented by the formula (2) are notespecially limited to the following, but include dimethylfluorophosphonate, diethyl fluorophosphonate, dibutyl fluorophosphonate,diphenyl fluorophosphonate, methyl ethyl fluorophosphonate, methylpropyl fluorophosphonate, methyl butyl fluorophosphonate, ethyl methylfluorophosphonate, propyl methyl fluorophosphonate, butyl methylfluorophosphonate, ethyl propyl fluorophosphonate, ethyl butylfluorophosphonate, propyl butyl fluorophosphonate, di(trifluoroethyl)fluorophosphonate, methyl trifluoroethyl fluorophosphonate, ethyltrifluoroethyl fluorophosphonate, propyl trifluoroethylfluorophosphonate, di(pentafluoropropyl) fluorophosphonate, methylpentafluoropropyl fluorophosphonate, ethyl pentafluoropropylfluorophosphonate, butyl pentafluoropropyl fluorophosphonate,difluorophenyl fluorophosphonate and ethyl fluorophenylfluorophosphonate.

Specific examples of compounds represented by the formula (3) are notespecially limited to the following, but include methyldifluorophosphinate, ethyl difluorophosphinate, butyldifluorophosphinate, phenyl difluorophosphinate, propyldifluorophosphinate, trifluoroethyl difluorophosphinate, fluoropropyldifluorophosphinate and fluorophenyl difluorophosphinate.

The content of an oxo-acid ester derivative of phosphorus in anonaqueous electrolyte solution is preferably 5% by mass or higher and60% by mass or lower. Making the content of the oxo-acid esterderivative of phosphorus to be 5 by mass or higher can improve the flameretardancy of the nonaqueous electrolyte solution. Making the content ofthe oxo-acid ester derivative of phosphorus to be 60% by mass or lowercan suppress a rise in the viscosity of the electrolyte solution, andcan hold the ionic conductivity at a reasonable one.

The disulfonate ester is at least one selected from a cyclic disulfonateester represented by the formula (4) and a linear disulfonate esterrepresented by the formula (5).

In the formula (4), Q represents an oxygen atom, a methylene group or asingle bond; A₁ represents a substituted or unsubstituted alkylene grouphaving 1 to 5 carbon atoms which may be branched, a carbonyl group, asulfinyl group, a substituted or unsubstituted perfluoroalkylene grouphaving 1 to 5 carbon atoms which may be branched, a substituted orunsubstituted fluoroalkylene group having 2 to 6 carbon atoms which maybe branched, a substituted or unsubstituted alkylene group having 1 to 6carbon atoms which contains an ether bond and may be branched, asubstituted or unsubstituted perfluoroalkylene group having 1 to 6carbon atoms which contains an ether bond and may be branched, or asubstituted or unsubstituted fluoroalkylene group having 2 to 6 carbonatoms which contains an ether bond and may be branched; and A₂represents a substituted or unsubstituted alkylene group, a substitutedor unsubstituted fluoroalkylene group, or an oxygen atom.

In the formula (5), R₁ and R₄ each independently represent an atom or agroup selected from a hydrogen atom, a substituted or unsubstitutedalkyl group having 1 to 5 carbon atoms, a substituted or unsubstitutedalkoxy group having 1 to 5 carbon atoms, a substituted or unsubstitutedfluoroalkyl group having 1 to 5 carbon atoms, a polyfluoroalkyl grouphaving 1 to carbon atoms, —SO₂X₁₁ (X₁₁ is a substituted or unsubstitutedalkyl group having 1 to 5 carbon atoms), —SY₁₁ (Y₁₁ is a substituted orunsubstituted alkyl group having 1 to 5 carbon atoms), —COZ (Z is ahydrogen atom or a substituted or unsubstituted alkyl group having 1 to5 carbon atoms), and a halogen atom; and R₂ and R₃ each independentlyrepresent an atom or a group selected from a substituted orunsubstituted alkyl group having 1 to 5 carbon atoms, a substituted orunsubstituted alkoxy group having 1 to 5 carbon atoms, a substituted orunsubstituted phenoxy group, a substituted or unsubstituted fluoroalkylgroup having 1 to 5 carbon atoms, a polyfluoroalkyl group having 1 to 5carbon atoms, a substituted or unsubstituted fluoroalkoxy group having 1to 5 carbon atoms, a polyfluoroalkoxy group having 1 to 5 carbon atoms,a hydroxyl group, a halogen atom, —NX₁₂X₁₃ (X₁₂ and X₁₃ are eachindependently a hydrogen atom or a substituted or unsubstituted alkylgroup having 1 to 5 carbon atoms), and —NY₁₂CONY₁₃Y₁₄ (Y₁₂ to Y₁₄ areeach independently a hydrogen atom or a substituted or unsubstitutedalkyl group having 1 to 5 carbon atoms).

Specific examples of compounds represented by the formula (4) are shownin Table 1, and specific examples of compounds represented by theformula (5) are shown in Table 2, but the present invention is notlimited thereto. These compounds may be used singly or concurrently intow or more.

TABLE 1 Compound Chemical No. Structure 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

TABLE 2 Compound Chemical No. Structure 101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

The compounds represented by the formula (4) or the formula (5) can beobtained, for example, by using a production method described inJP5-44946B.

The content of a disulfonate ester in a nonaqueous electrolyte solutionis preferably 0.05% by mass or higher and 10% by mass or lower, and morepreferably 0.1% by mass or higher and 5% by mass or lower. When thecontent of the disulfonate ester is 0.05% by mass or higher, thereductive decomposition of an oxo-acid ester derivative of phosphoruscan be suppressed; and when the content is 10% by mass or lower, sincean excessive increase in film thickness is prevented, a decrease in thecapacity can be suppressed. When the content of the disulfonate ester is0.1% by mass or higher, the reductive decomposition of the oxo-acidester derivative of phosphorus can be more easily suppressed over a longperiod. When the content of the disulfonate ester is 5% by mass orlower, the film thickness can be made in a suitable range, an increasein the resistance can be prevented, and decreases in the capacity andthe maintenance rate can be suppressed more.

The nonaqueous electrolyte solution according to the exemplaryembodiment may contain an aprotic solvent. The aprotic solvent is notespecially limited, but examples thereof include cyclic carbonates suchas propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate(BC) and vinylene carbonate (VC), linear carbonates such as dimethylcarbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC)and dipropyl carbonate (DPC), aliphatic carboxylate esters such asmethyl formate, methyl acetate and ethyl propionate, γ-lactones such asγ-butyrolactone, linear ethers such as 1,2-ethoxyethane (DEE) andethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide,acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile,nitromethane, ethylmonoglyme, phosphate triesters, trimethoxymethane,dioxolane derivatives, sulfolane, methylsulfolane,1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylenecarbonate derivatives, tetrahydrofuran derivatives, ethyl ether,anisole, N-methylpyrrolidone, and fluorocarboxylate esters. Theseaprotic solvents may be used singly or as a mixture of two or more.

The nonaqueous electrolyte solution according to the exemplaryembodiment may further contain a cyclic carbonate ester containing ahalogen. Since the addition of a cyclic carbonate ester containing ahalogen improves the ionic conductivity of the nonaqueous electrolytesolution and also contributes to the film formation, the maintenance ofbattery characteristics and the flame retardancy over a long period canbe attained. An example of the cyclic carbonate ester containing ahalogen includes a fluorine-containing carbonate. Thefluorine-containing carbonate includes a linear one and a cyclic one,and a cyclic fluorine-containing carbonate (hereinafter, alsoabbreviated to a fluorine-containing cyclic carbonate) is preferable.

The fluorine-containing cyclic carbonate is not especially limited, buta compound in which a part of propylene carbonate, vinylene carbonate orvinyl ethylene carbonate is fluorinated, or the like may be used. Morespecific examples thereof include 4-fluoro-1,3-dioxolan-2-one(fluoroethylene carbonate, hereinafter, also referred to as FEC), (cis-or trans-) 4,5-difluoro-1,3-dioxolan-2-one (difluoroethylene carbonate),4,4-difluoro-1,3-dioxolan-2-one, 4-fluoro-5-methyl-1,3-dioxolan-2-one,and a fluoropropylene carbonate. These may be used singly or as amixture of two or more. Above all, the fluoroethylene carbonate ispreferable.

The content of a cyclic carbonate ester containing a halogen in anonaqueous electrolyte solution is preferably 0.5% by mass or higher and20% by mass or lower, and more preferably 0.5% by mass or higher and 10%by mass or lower. When the content of the cyclic carbonate estercontaining a halogen is 0.5% by mass or higher, the reductivedecomposition of an oxo-acid ester derivative of phosphorus can besuppressed; and when the content is 20% by mass or lower, an increase inthe resistance due to a film originated from the cyclic carbonate estercontaining a halogen can be suppressed, and a decrease in the capacitycan be suppress. When the content of the cyclic carbonate estercontaining a halogen is 10% by mass or lower, the film thickness of thefilm can be made in a suitable range, further an increase in theresistance can be prevented, and decreases in the capacity and themaintenance rate can be suppressed more.

An electrolyte contained in the nonaqueous electrolyte solutionaccording to the exemplary embodiment is not especially limited to thefollowing, but examples thereof include LiPF₆, LiBF₄, LiAsF₆, LiSbF₆,LiClO₄, LiAlCl₄, LiN(C_(n)F_(2n+1)SO₂)(C_(m)F_(2m+1)SO₂) (n and m arenatural numbers), and LiCF₃SO₃.

In the lithium ion secondary battery having a nonaqueous electrolytesolution according to the exemplary embodiment, as a negative electrodeactive substance, one or two or more substances can be used which areselected from the group consisting of, for example, metallic lithium,lithium alloys and materials capable of adsorbing and releasing lithium.The material adsorbing and releasing lithium ions includes carbonmaterials and oxides.

The carbon materials may be graphite, amorphous carbon, diamond-likecarbon, carbon nanotubes and the like to adsorb lithium, and compositematerials thereof. Particularly graphite has a high electronconductivity, is excellent in the adhesivity with a current collectorcomposed of a metal such as copper, and the voltage flatness, andcontains only a low content of impurities because of being formed at ahigh processing temperature, which are preferably advantageous forimprovement of the negative electrode performance. A composite materialof a high-crystalline graphite and a low-crystalline amorphous carbon,and the like can also be used.

The oxide may be one of silicon oxide, tin oxide, indium oxide, zincoxide, lithium oxide, phosphoric acid and boric acid, or may be acomposite thereof, which preferably contains especially silicon oxide.The structure is preferably in an amorphous state. This is becausesilicon oxide is stable and causes no reaction with other compounds, andbecause the amorphous structure introduces no deteriorations caused bynon-uniformity such as crystal grain boundaries and defects.Film-formation methods usable are ones such as a vapor-depositionmethod, a CVD method and a sputtering method.

The lithium alloy is constituted of lithium and metals alloyable withlithium. The lithium alloy is constituted of a binary, ternary, or moremulti-metal alloy of metals such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca,Hg, Pd, Pt, Te, Zn and La, with lithium. Metallic lithium and lithiumalloys are especially preferable in an amorphous state. This is becausethe amorphous structure hardly causes deteriorations caused bynon-uniformity such as crystal grain boundaries and defects.

Metallic lithium and lithium alloys are suitably formed by a systemincluding a melt cooling system, a liquid quenching system, an atomizingsystem, a vacuum vapor-deposition system, a sputtering system, a plasmaCVD system, an optical CVD system, a thermal CVD system and a sol-gelsystem.

In the lithium ion secondary battery according to the exemplaryembodiment, examples of a positive electrode active substance includelithium-containing composite oxides such as LiCoO₂, LiNiO₂ and LiMn₂O₄.A transition metal part of the lithium-containing composite oxides maybe replaced by another element.

A lithium-containing composite oxide having a plateau of 4.5 V or highervs. a counter electrode potential of metallic lithium may be used. Thelithium-containing composite oxide is exemplified by a spinel-typelithium-manganese composite oxide, an olivine-type lithium-containingcomposite oxide and an inverse-spinel-type lithium-containing compositeoxide. An example of the lithium-containing composite oxide include acompound represented by Li_(a)(M_(x)Mn_(2−x))O₄ (here, 0<x<2; 0<a<1.2;and M is at least one selected from the group consisting of Ni, Co, Fe,Cr and Cu).

The nonaqueous electrolyte solution according to the exemplaryembodiment may be gelated with a gelling component. That is, thenonaqueous electrolyte solution according to the exemplary embodimentincludes gelatinous materials. Examples of the gelling component includepolymer components. Examples of the polymer component include monomers,oligomers and copolymerized oligomers having two or more thermallypolymerizable polymerization groups in one molecule thereof. Examples ofthe polymer component include compounds to form acrylic polymersincluding difunctional acrylates such as ethylene glycol diacrylate,diethylene glycol diacrylate, triethylene glycol diacrylate,tetraethylene glycol diacrylate, propylene diacrylate, dipropylenediacrylate, tripropyrene diacrylate, 1,3-butanediol diacrylate,1,4-butanediol diacrylate and 1,6-hexanediol diacrylate, trifunctionalacrylates such as trimethylolpropane triacrylate and pentaerythritoltriacrylate, tetrafunctional acrylates such as ditrimethylolpropanetetraacrylate and pentaerythritol tetraacrylate, and methacrylatescorresponding thereto. Additional examples of the polymer componentinclude monomers such as urethane acrylates and urethane methacrylate,copolymerized oligomers thereof and copolymerized oligomers withacrylonitrile.

Gelling components also usable are polymers having a gelling power, suchas polyvinylidene fluoride, polyethylene oxide and polyacrylonitrile.

Gelling components are not limited to the above-mentioned monomers,oligomers and polymers, and can be used without any especial problem aslong as being capable of gelating a nonaqueous electrolyte solution. Thegelling component may be used singly or concurrently in tow or more.

As required, benzoins, peroxides and the like can be used as athermopolymerization initiator, but the thermopolymerization initiatoris not limited to these.

The nonaqueous electrolyte solution according to the exemplaryembodiment can reduce the amount of gases generated in the initialcharge, which is preferable also from the viewpoint of the safety andthe production process. The reason is presumed to be that since thecoexistence of an oxo-acid ester derivative of phosphorus and adisulfonate ester in a nonaqueous electrolyte solution can form an SEIhaving a part of the oxo-acid ester derivative of phosphorusincorporated therein by a reaction mechanism different from that of theSEI formation in a nonaqueous electrolyte solution containing only adisulfonate ester, the generation amount of gases is reduced. Judgingfrom that on an SEI formed in such a way, the reduction of an oxo-acidester derivative of phosphorus present in a nonaqueous electrolytesolution can be suppressed, it is presumed that the SEI by disulfonateester having the oxo-acid ester derivative of phosphorus incorporatedtherein is firmly formed, and the suppression effect of the reductivedecomposition of the oxo-acid ester derivative of phosphorus andcomponents in the nonaqueous electrolyte solution may possibly beenhanced. It is conceivable that the effect can achieve the suppressionof a resistance rise and the suppression of gas generation in thelong-term cycle, leading to good life characteristics. Further since theoxo-acid ester derivative of phosphorus can be suppressed in thereductive decomposition over a long period, high safety can be attainedover a long period.

The battery constitution of the lithium ion secondary battery accordingto the present embodiment is not especially limited, but includes, forexample, laminated types and wound types. An armor body is notespecially limited, but includes, for example, aluminum laminate filmsand metal cans. The battery capacity is not limited.

With respect to the device according to the exemplary embodiment, in theexemplary embodiment and Examples, mainly lithium ion secondarybatteries have been and will be described. However, the presentinvention is not especially limited thereto, and the nonaqueouselectrolyte solution according to the exemplary embodiment can beapplied also to capacitors.

EXAMPLES

Hereinafter, the present invention will be described in detail by way ofExamples and by reference to drawings, but the present invention is notlimited to the Examples.

FIG. 1 is a schematic diagram illustrating a constitution of a positiveelectrode of a lithium ion secondary battery; and FIG. 1(a) is a plandiagram of the positive electrode, and FIG. 1(b) is a side diagram ofthe positive electrode.

FIG. 2 is a schematic diagram illustrating a constitution of a negativeelectrode of a lithium ion secondary battery; and FIG. 2(a) is a plandiagram of the negative electrode, and FIG. 2(b) is a side diagram ofthe negative electrode.

FIG. 3 is a diagram illustrating a constitution of a battery elementafter being wound of a lithium ion secondary battery.

Example 1

First, fabrication of a positive electrode 1 will be described byreference to FIG. 1. 85% by mass of LiMn₂O₄ as a positive electrodeactive substance, 7% by mass of an acetylene black as a conductiveauxiliary material and 8% by mass of a polyvinylidene fluoride as abinder were mixed; and N-methylpyrrolidone was added to the mixture, andfurther mixed to thereby prepare a positive electrode slurry. Thepositive electrode slurry was applied on both surfaces of an Al foil 2having a thickness of 20 μm to become a current collector by a doctorblade method so that the thickness after a roll pressing process became160 μm, dried at 120° C. for 5 min, and subjected to the roll pressingprocess to thereby form positive electrode active substance layers 14.Positive electrode active substance-unapplied portions 5, on which nopositive electrode active substance was applied, were provided on eithersurface of both end parts of the foil. A positive electrode conductivetab 6 was provided by welding on one of the positive electrode activesubstance-unapplied portions 5. A positive electrode activesubstance-one surface-applied portion 4, which was a portion of onesurface having the positive electrode active substance applied only onthe one surface, was provided adjacent to the positive electrode activesubstance-unapplied portion 5 provided with the positive electrodeconductive tab 6. Here, reference numeral 3 was a positive electrodeactive substance-both surface-applied portion. A positive electrode 1was thus fabricated by the above method.

Then, fabrication of a negative electrode 7 will be described byreference to FIG. 2. 90% by mass of a graphite as a negative electrodeactive substance, 1% by mass of an acetylene black as a conductiveauxiliary material and 9% by mass of a polyvinylidene fluoride as abinder were mixed; and N-methylpyrrolidone was added to the mixture, andfurther mixed to thereby prepare a negative electrode slurry. Thenegative electrode slurry was applied on both surfaces of a Cu foil 8having a thickness of 10 μm to become a current collector by a doctorblade method so that the thickness after a roll pressing process became120 μm, dried at 120° C. for 5 min, and subjected to the roll pressingprocess to thereby form negative electrode active substance layers 15.Negative electrode active substance-unapplied portions 11, on which nonegative electrode active substance was applied, were provided on eithersurface of both end parts of the foil. A negative electrode conductivetab 12 was provided by welding on one of the negative electrode activesubstance-unapplied portions 11. A negative electrode activesubstance-one surface-applied portion 10, which was a portion of onesurface having the negative electrode active substance applied only onthe one surface, was provided adjacent to the negative electrode activesubstance-unapplied portion 11 provided with the negative electrodeconductive tab 12. Here, reference numeral 9 was a negative electrodeactive substance-both surface-applied portion. A negative electrode 7was thus fabricated by the above method.

Fabrication of a battery element will be described by reference to FIG.3. A fused and cut portion of two sheets of a separator 13 composed of apolypropylene microporous membrane having a membrane thickness of 25 μmand a porosity of 55% and being subjected to a hydrophilicizingtreatment was fixed and wound to a winding core of a winding apparatus,and front ends of the positive electrode and the negative electrode wereintroduced. The side of the positive electrode opposite to theconnection portion of the positive electrode conductive tab 6 was madeto be the front end side of the positive electrode; and the side of theconnection portion of the negative electrode conductive tab 12 was madeto be the front end side of the negative electrode. The negativeelectrode was disposed between the two sheets of the separator 13, andthe positive electrode was disposed on the upper surface of theseparator 13; and the both were wound by rotating the winding core tothereby form a battery element (hereinafter, referred to as a jelly roll(J/R)).

The J/R was accommodated in an embossed laminate armor body; thepositive electrode conductive tab 6 and the negative electrodeconductive tab 12 were led out; and one side of the laminate armor bodywas folded back, and thermally fused with a portion for solutioninjection being left unfused.

A nonaqueous electrolyte solution was prepared which contained 1.2 mol/Lof LiPF₆ as a supporting salt, 5% by mass of tri(2,2,2-trifluoroethyl)phosphate as an oxo-acid ester derivative of phosphorus, and 2% by massof the compound No. 2 in Table 1 as a disulfonate ester as an additive.An aprotic solvent of ethylene carbonate (EC)/diethyl carbonate(DEC)=30/70 (volume ratio) was used.

Then, the nonaqueous electrolyte solution was injected through thelaminate solution injection portion, and impregnated under vacuum. Then,the solution injection portion was thermally fused to thereby obtain alithium ion secondary battery.

A discharge capacity acquired when the obtained battery was CC-CVcharged (constant current-constant voltage charge, charge conditions: aCC current of 0.2 C, a CV time of 1.5 hours, and a temperature of 20°C.) to a battery voltage of 4.2 V, and thereafter discharged at 0.2 C toa battery voltage of 3.0 V was defined as an initial capacity. Theproportion of the acquired initial capacity to a design capacity wasdefined as an initial capacity (%).

A cycle test of the obtained battery was carried out by carrying outCC-CV charge at an upper-limit voltage of 4.2 V, a current of 1 C and aCV time of 1.5 hours, and CC discharge at a lower-limit voltage of 3.0 Vand a current of 1 C, and both at 45° C. The capacity maintenance ratewas defined as a proportion of a discharge capacity at the 1,000th cycleto a discharge capacity at the first cycle. The capacity maintenancerate is shown in Table 3.

A combustion test was carried out by placing a battery after the cycletest 10 cm above the tip end of a flame of a gas burner. Then, the flameretardancy was determined as follows from a state of a nonaqueouselectrolyte solution burning. A case where the nonaqueous electrolytesolution was not ignited was indicated as ⊙; a case where even ifignition was caused, the fire extinguished 2 to 3 sec after theignition, as ◯; a case where even if ignition was caused, the fireextinguished within 10 sec, as Δ; and a case where the fire did notextinguished within 10 sec and burning continued, as x.

Example 2

In Example 2, a battery was fabricated and evaluated as in the case ofExample 1, except for preparing a nonaqueous electrolyte solution bymixing 10% by mass of tri(2,2,2-trifluoroethyl) phosphate (hereinafter,referred to also as PTTFE).

Example 3

In Example 3, a battery was fabricated and evaluated as in the case ofExample 1, except for preparing a nonaqueous electrolyte solution bymixing 20% by mass of PTTFE.

Example 4

In Example 4, a battery was fabricated and evaluated as in the case ofExample 1, except for preparing a nonaqueous electrolyte solution bymixing 40% by mass of PTTFE.

Example 5

In Example 5, a battery was fabricated and evaluated as in the case ofExample 3, except for preparing a nonaqueous electrolyte solution byaltering PTTFE to di(trifluoroethyl) fluorophosphonate.

Example 6

In Example 6, a battery was fabricated and evaluated as in the case ofExample 3, except for preparing a nonaqueous electrolyte solution byaltering PTTFE to trifluoroethyl difluorophosphinate.

Example 7

In Example 7, a battery was fabricated and evaluated as in the case ofExample 3, except for preparing a nonaqueous electrolyte solution byusing the compound No. 101 in Table 2 in place of the compound No. 2 asan additive.

Example 8

In Example 8, a battery was fabricated and evaluated as in the case ofExample 3, except for preparing a nonaqueous electrolyte solution bymixing 3% by mass of fluoroethylene carbonate (FEC) in addition to thecompound No. 2 as an additive.

Example 9

In Example 9, a battery was fabricated and evaluated as in the case ofExample 8, except for preparing a nonaqueous electrolyte solution byusing the compound No. 101 in Table 2 in place of the compound No. 2 asan additive.

Example 10

In Example 10, a battery was fabricated and evaluated as in the case ofExample 8, except for preparing a nonaqueous electrolyte solution byaltering the amount of PTTFE to 60% by mass.

Comparative Example 1

In Comparative Example 1, a battery was fabricated and evaluated as inthe case of Example 3, except for preparing a nonaqueous electrolytesolution by mixing 3% by mass of 1,3-propane sultone (PS) in place ofthe compound No. 2 as an additive.

Comparative Example 2

In Comparative Example 2, a battery was fabricated and evaluated as inthe case of Example 3, except for preparing a nonaqueous electrolytesolution by mixing 3% by mass of vinylene carbonate (VC) in place of thecompound No. 2 as an additive.

Comparative Example 3

In Comparative Example 3, a battery was fabricated and evaluated as inthe case of Example 3, except for preparing a nonaqueous electrolytesolution by mixing 3% by mass of fluoroethylene carbonate in place ofthe compound No. 2 as an additive.

Comparative Example 4

In Comparative Example 4, a battery was fabricated and evaluated as inthe case of Example 3, except for preparing a nonaqueous electrolytesolution by mixing 3% by mass of vinylene carbonate and 3% by mass offluoroethylene carbonate in place of the compound No. 2 as additives.

Comparative Example 5

In Comparative Example 5, a battery was fabricated and evaluated as inthe case of Example 10, except for preparing a nonaqueous electrolytesolution by mixing 3% by mass of vinylene carbonate in place of thecompound No. 2 as an additive.

The results of the initial capacity, the capacity maintenance rate andthe flame retardancy in Examples 1 to 10 and Comparative Examples 1 to 5are shown in Table 3.

TABLE 3 Negative Electrode Active Oxo-Acid Ester Addition InitialCapacity Substance/ Derivative of Amount Capacity Maintenance FlameElectrolyte Phosphorus (mass %) Additive (%) Rate (%) Retardancy Example1 graphite/ tri(trifluoroethyl) 5 No. 2 93 82 ◯ liquid phosphate Example2 graphite/ tri(trifluoroethyl) 10 No. 2 91 75 ◯ liquid phosphateExample 3 graphite/ tri(trifluoroethyl) 20 No. 2 91 75 ⊙ liquidphosphate Example 4 graphite/ tri(trifluoroethyl) 40 No. 2 87 67 ⊙liquid phosphate Example 5 graphite/ Di(trifluoroethyl) 20 No. 2 93 81 ⊙liquid fluorophosphonate Example 6 graphite/ Trifluoroethyl 20 No. 2 9382 ⊙ liquid difluorophosphinate Example 7 graphite/ tri(trifluoroethyl)20 No. 101 90 74 ⊙ liquid phosphate Example 8 graphite/tri(trifluoroethyl) 20 No. 2 + 85 84 ⊙ liquid phosphate FEC Example 9graphite/ tri(trifluoroethyl) 20 No. 101 + 88 85 ⊙ liquid phosphate FECExample 10 graphite/ tri(trifluoroethyl) 60 No. 2 + 76 75 ⊙ liquidphosphate FEC Comparative graphite/ tri(trifluoroethyl) 20 PS 93 54 ΔExample 1 liquid phosphate Comparative graphite/ tri(trifluoroethyl) 20VC 91 56 Δ Example 2 liquid phosphate Comparative graphite/tri(trifluoroethyl) 20 FEC 89 36 X Example 3 liquid phosphateComparative graphite/ tri(trifluoroethyl) 20 VC + FEC 81 59 Δ Example 4liquid phosphate Comparative graphite/ tri(trifluoroethyl) 60 VC + FEC53 11 ◯ Example 5 liquid phosphate

No. 2 in the column of an additive in Table 3 indicates the compound No.2 in Table 1; No. 101, the compound No. 101 in Table 2; FEC,fluoroethylene carbonate; PS, 1,3-propane sultone; and VC, vinylenecarbonate.

As shown in Examples 1 to 4, if the content of an oxo-acid esterderivative of phosphorus was increased, the flame retardancy of anonaqueous electrolyte solution became very good, and no ignitionoccurred, and even if ignition occurred, the fire extinguished 2 to 3sec after the ignition.

Comparing Examples 3 and 5 to 7 with Comparative Examples 1 and 2, whichall contained the same amount of a phosphate ester, the capacitymaintenance rate was good and the flame retardancy was very good forExamples 3 and 5 to 7, in which a disulfonate ester was added. Bycontrast, the capacity maintenance rate after the cycle decreased, andthe flame retardancy was low in Comparative Examples 1 and 2.

Further for Comparative Example 4, in which a fluoroethylene carbonatewas added, the capacity maintenance rate and the flame retardancy wereslightly improved, but the flame retardancy could not be said to besufficient. By contrast, for Examples 8 and 9, the capacity maintenancerate and the flame retardancy were both good. Also from the comparisonof Example 10 with Comparative Example 5, in both of which the contentof tri(trifluoroethyl) phosphate used as an electrolyte solution solventwas made large, Example 10 was better in both the capacity maintenancerate and the flame retardancy due to the effect of a disulfonate ester.

From the above, the SEI formation by a disulfonate ester could suppressthe reductive decomposition of an oxo-acid ester derivative ofphosphorus over a long period, could provide a good capacity maintenancerate, and could further provide a high flame retardancy. Further,incorporation of a halogen-containing cyclic carbonate ester in additionto a disulfonate ester in an electrolyte solution formed a good SEI, andconsequently could further suppress the reductive decomposition of theoxo-acid ester derivative of phosphorus, further could reduce the gasgeneration amount in the cycle, and then could provide a good capacitymaintenance rate.

Example 11

In Example 11, an example will be described in which a nonaqueouselectrolyte solution was gelated with a gelling component to be therebymade into a gel electrolyte. A battery was fabricated and evaluated asin Example 1, except for making a secondary battery having a gelelectrolyte by using the following pre-gel solution.

The pre-gel solution was prepared by mixing 1.2 mol/L of LiPF₆ as asupporting salt, EC/DEC=30/70 (volume ratio) as aprotic solvents, 20% bymass of tri(trifluoroethyl) phosphate as an oxo-acid ester derivative ofphosphorus, 2% by mass of the compound No. 2 in Table 1 as a disulfonateester as an additive, 3.8% by mass of triethylene glycol diacrylate as agelling component, 1% by mass of trimethylolpropane triacrylate as agelling component, and 0.5% by mass of t-butyl peroxypivalate as apolymerization initiator.

Then, the pre-gel solution was injected through the solution injectionportion, and impregnated under vacuum. Then, the solution injectionportion was thermally fused. Then, the pre-gel solution was polymerizedat 80° C. for 2 hours to be gelated to thereby obtain a lithium ionsecondary battery (lithium polymer battery) having a gelatinousnonaqueous electrolyte solution.

Example 12

In Example 12, a battery was fabricated and evaluated as in the case ofExample 11, except for preparing a pre-gel solution by mixing 3% by massof fluoroethylene carbonate in addition to the compound No. 2 as anadditive.

Comparative Example 6

In Comparative Example 6, a battery was fabricated and evaluated as inthe case of Example 12, except for preparing a pre-gel solution bymixing 3% by mass of vinylene carbonate in place of the compound No. 2.

The results of the initial capacity, the capacity maintenance rate andthe flame retardancy in Examples 11 and 12 and Comparative Example 6 areshown in Table 4.

TABLE 4 Ca- Negative pacity Electrode Main- Active Oxo-Acid EsterAddition Initial tenance Flame Substance/ Derivative of Amount CapacityRate Retard- Electrolyte Phosphorus (mass %) Additive (%) (%) ancyExample 11 graphite/ tri(trifluoroethyl) 20 No. 2 73 56 ◯ polymerphosphate Example 12 graphite/ tri(trifluoroethyl) 20 No. 2 + 71 63 ◯polymer phosphate FEC Comparative graphite/ tri(trifluoroethyl) 20 VC +65 40 X Example 6 polymer phosphate FEC

No. 2 in the column of an additive in Table 4 indicates the compound No.2 in Table 1; FEC, fluoroethylene carbonate; and VC, vinylene carbonate.

From Table 4, even in the case of a gelatinous nonaqueous electrolytesolution, the SEI formation by a disulfonate ester could suppress thereductive decomposition of an oxo-acid ester derivative of phosphorusover a long period, could provide a good capacity maintenance rate, andcould further provide a high flame retardancy.

Example 13

In Example 13, an example will be described in which a negativeelectrode active substance containing a silicon-based material was used.A battery was fabricated and evaluated as in Example 3, except formaking a secondary battery having a negative electrode having a negativeelectrode active substance as described below.

First, 90% by mass of silicon as a negative electrode active substance,1% by mass of an acetylene black as a conductive auxiliary material and9% by mass of a polyimide as a binder were mixed; andN-methylpyrrolidone was added to the mixture, and further mixed tothereby prepare a negative electrode slurry. The negative electrodeslurry was applied on both surfaces of a Cu foil having a thickness of10 μm to become a current collector by a doctor blade method so that thethickness after a roll pressing process became 80 μm, dried at 120° C.for 5 min, subjected to the roll pressing process, and furtheradditionally dried at 300° C. for 10 min to thereby form negativeelectrode active substance layers 15.

Example 14

In Example 14, a battery was fabricated and evaluated as in the case ofExample 13, except for preparing a nonaqueous electrolyte solution bymixing 3% by mass of fluoroethylene carbonate in addition to thecompound No. 2 as an additive.

Comparative Example 7

In Comparative Example 7, a battery was fabricated and evaluated as inthe case of Example 14, except for preparing a nonaqueous electrolytesolution by mixing 3% by mass of vinylene carbonate in place of thecompound No. 2 as an additive.

Cycle tests of Examples 13 and 14 and Comparative Example 7 were carriedout by carrying out CC-CV charge at an upper-limit voltage of 4.2 V, acurrent of 1 C and a CV time of 1.5 hours, and CC discharge at alower-limit voltage of 3.0 V and a current of 1 C, and both at 45° C.The capacity maintenance rate was defined as a proportion of a dischargecapacity at the 200th cycle to a discharge capacity at the first cycle.

The results of the initial capacity, the capacity maintenance rate andthe flame retardancy in Examples 13 and 14 and Comparative Example 7 areshown in Table 5.

TABLE 5 Ca- Negative pacity Electrode Main- Active Oxo-Acid EsterAddition Initial tenance Flame Substance/ Derivative of Amount CapacityRate Retard- Electrolyte Phosphorus (mass %) Additive (%) (%) ancyExample 13 silicon/ tri(trifluoroethyl) 20 No. 2 76 68 ◯ liquidphosphate Example 14 silicon/ tri(trifluoroethyl) 20 No. 2 + 69 72 ◯liquid phosphate FEC Comparative silicon/ tri(trifluoroethyl) 20 VEC +68 47 Δ Example 7 liquid phosphate FEC

No. 2 in the column of an additive in Table 5 indicates the compound No.2 in Table 1; FEC, fluoroethylene carbonate; and VC, vinylene carbonate.

From Table 5, even when a silicon material was used in place of graphiteas a negative electrode active substance, the SEI formation by adisulfonate ester could suppress the reductive decomposition of anoxo-acid ester derivative of phosphorus, could provide a good capacitymaintenance rate, and could further provide a high flame retardancy.

It can be confirmed from the above that the exemplary embodiment couldprovide a nonaqueous electrolyte solution having a high flame retardancyover a long period, and having a good capacity maintenance rate.

The present application claims the priority to Japanese PatentApplication No. 2010-027056, filed on Feb. 10, 2010, the disclosure ofwhich is all incorporated herein.

Hitherto, the present invention has been described by reference to theexemplary embodiment and Examples, but the present invention is notlimited to the exemplary embodiment and the Examples. In theconstitution and the detail of the present invention, various changesand modifications understandable to those skilled in the art may be madewithin the scope of the present invention.

REFERENCE SIGNS LIST

-   1 POSITIVE ELECTRODE-   2 Al FOIL-   3 POSITIVE ELECTRODE ACTIVE SUBSTANCE-BOTH SURFACE-APPLIED PORTION-   4 POSITIVE ELECTRODE ACTIVE SUBSTANCE-ONE SURFACE-APPLIED PORTION-   5 POSITIVE ELECTRODE ACTIVE SUBSTANCE-UNAPPLIED PORTION-   6 POSITIVE ELECTRODE CONDUCTIVE TAB-   7 NEGATIVE ELECTRODE-   8 Cu FOIL-   9 NEGATIVE ELECTRODE ACTIVE SUBSTANCE-BOTH SURFACE-APPLIED PORTION-   10 NEGATIVE ELECTRODE ACTIVE SUBSTANCE-ONE SURFACE-APPLIED PORTION-   11 NEGATIVE ELECTRODE ACTIVE SUBSTANCE-UNAPPLIED PORTION-   12 NEGATIVE ELECTRODE CONDUCTIVE TAB-   13 SEPARATOR-   14 POSITIVE ELECTRODE ACTIVE SUBSTANCE LAYER-   15 NEGATIVE ELECTRODE ACTIVE SUBSTANCE LAYER

The invention claimed is:
 1. A nonaqueous electrolyte solution,comprising: a lithium salt; at least one oxo-acid ester derivative ofphosphorus selected from halogen-substituted phosphate estersrepresented by formula (1); at least one linear disulfonate esterrepresented by the formula (5); and 0.5% by mass or more and 20% by massor less of a cyclic carbonate ester containing a halogen:

in the formula (1), R₁₁, R₁₂ and R₁₃ each independently represent anygroup selected from an alkyl group, an aryl group, an alkenyl group, acyano group, a phenyl group, an amino group, a nitro group, an alkoxygroup and a cycloalkyl group, and a halogen-substituted group thereof;where any two or all of R₁₁, R₁₂ and R₁₃ may be bonded to form a cyclicstructure, and where at least one of R₁₁, R₁₂ or R₁₃ is ahalogen-substituted group;

in the formula (5), R₁ and R₄ each independently represent an atom or agroup selected from a hydrogen atom, a substituted or unsubstitutedalkyl group having 1 to 5 carbon atoms, a substituted or unsubstitutedalkoxy group having 1 to 5 carbon atoms, a substituted or unsubstitutedfluoroalkyl group having 1 to 5 carbon atoms, a polyfluoroalkyl grouphaving 1 to 5 carbon atoms, —SO₂X₁₁, where X₁₁ is a substituted orunsubstituted alkyl group having 1 to 5 carbon atoms, —SY₁₁, where Y₁₁is a substituted or unsubstituted alkyl group having 1 to 5 carbonatoms, —COZ, where Z is a hydrogen atom or a substituted orunsubstituted alkyl group having 1 to 5 carbon atoms, and a halogenatom; and R₂ and R₃ each independently represent an atom or a groupselected from a substituted or unsubstituted alkyl group having 1 to 5carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 5carbon atoms, a substituted or unsubstituted phenoxy group, asubstituted or unsubstituted fluoroalkyl group having 1 to 5 carbonatoms, a polyfluoroalkyl group having 1 to 5 carbon atoms, a substitutedor unsubstituted fluoroalkoxy group having 1 to 5 carbon atoms, apolyfluoroalkoxy group having 1 to 5 carbon atoms, a hydroxyl group, ahalogen atom, —NX₁₂X₁₃, where X₁₂ and X₁₃ are each independently ahydrogen atom or a substituted or unsubstituted alkyl group having 1 to5 carbon atoms, and —NY₁₂CONY₁₃Y₁₄, where Y₁₂ to Y₁₄ are eachindependently a hydrogen atom or a substituted or unsubstituted alkylgroup having 1 to 5 carbon atoms.
 2. The nonaqueous electrolyte solutionaccording to claim 1, comprising 5% by mass or more and 60% by mass orless of the oxo-acid ester derivative of phosphorus.
 3. The nonaqueouselectrolyte solution according to claim 1, comprising 0.05% by mass ormore and 10% by mass or less of the disulfonate ester.
 4. A lithium ionsecondary battery, comprising a nonaqueous electrolyte solutionaccording to claim
 1. 5. A capacitor, comprising a nonaqueouselectrolyte solution according to claim 1.